The present invention relates to a three point coupling or implement hitch arrangement for a tractor and the control for lifting and tilting the draft arms of a three point hitch.
The prior art includes numerous examples of tractor mounted three point hitch arrangements which are commonly used to support, adjust and pull various agricultural and industrial implements. Typical agricultural implements which are generally mounted on a three point hitch include plows, disks, cultivators and rotary hoes, which may be interchanged for use. A three point hitch assembly normally includes a pair of drawbar links or draft arms which are pivotally supported in spaced relation at their forward ends on the tractor. The arms are raised or lowered about their forward pivotal axes by a hydraulic lift assembly mounted on the tractor. The conventional three point hitch arrangement includes a pair of upper arms mounted in spaced relation on a transverse rock shaft. The upper arms extend from the rock shaft above the draft arms which are pivotally connected at their forward ends on a frame assembly attached to the tractor. Draft arm links are connected between the free ends of the upper arms and the draft arms and a lift cylinder is connected between the frame assembly and the rock shaft to raise or lower the free ends of the draft arms. One of the draft links may be replaced with a leveling cylinder to provide relative adjustment of the draft arms or leveling of the draft arms.
U.S. Pat. No. 3,750,757 discloses a three point hitch arrangement of this general type wherein the draft arms are raised, lowered or tilted by hydraulic lift cylinders. A lift cylinder is pivotally supported above each of the draft arms on a plate mounted on the back of the tractor. The rod portion of the lift cylinders are mounted to the midportion of the draft arms for controlling the angular position of the draft arms about the forward transverse pivotal axes. The lift cylinders are hydraulically connected in series, such that upon movement of one of the cylinders there is a transfer of fluid between the two cylinders to cause the second cylinder to move with the first cylinder with the volume of hydraulic fluid transferred from one cylinder to the other being variable to vary the relative inclination of the draft arms. As disclosed, this is a relatively complex system wherein the unequal movement of the cylinders and draft arms is compensated by rods connected to the draft arms which are connected to links, levers and valves. The system includes a transverse stabilization distributor which senses a pressure drop in the line interconnecting the hydraulic cylinders and compensating for a load shift. It is the primary object of the present invention to simplify the control of the draft arms to provide lift and tilt movement of the draft arms without a complex mechanical and hydraulic control.
As described below, the hydraulic lift arrangement of the present invention preferably includes two lift cylinders which are connected in series wherein the area of the rod end of the first cylinder is equal to the area of the head end of the second cylinder, such that the cylinders may be actuated to move in unison without complex hydraulic and mechanical controls as described in the above-referenced U.S. patent. As will be understood, however, the prior art also includes hydraulic lift arrangements and controls having hydraulic cylinders connected in series, wherein the displacement of the cylinders are matched so that movement of any piston rod is accompanied by equal movement of the other piston rods as, for example, disclosed in U.S. Pat. No. 3,627,053. Reference is also made to U.S. Pat. No. 3,762,480 which discloses a hydraulic control apparatus for maintaining an agricultural implement level with the ground having hydraulic cylinders connected in parallel of unequal sizes.
The third connection of the three point coupling or hitch arrangement is provided by an arm or link pivotally supported on the back of the tractor above and between the draft arms. Where pitch adjustment is desired, a turnbuckle may be utilized for manual pitch adjustment of the implement or a hydraulic pitch cylinder has been used for pitch adjustment of the implement. As will now be understood, the need remains for a three point coupling or implement hitch arrangement for a tractor, which is relatively simple in construction and control, wherein the draft arms may be independently controlled to lift or tilt the implement.